The specific receptor for antigen on T lymphocytes, the TcR (), is a heterodimeric protein with motifs that are similar to immunoglobulin molecules, but whose structure is encoded by a different set of V, J, D, and C genes. Moreover, T cells consist of two subsets carrying different receptors, that have been designated α/β and γ/δ.
A minority of T cells express a TcR consisting of γ and δ chains and those cells are primarily CD4⁺. These chains are encoded by very few genes; the γ/δ repertoire is accordingly very limited. The γ gene cluster consists of seven V genes, two J genes, and four C genes. The δ genes are interspersed within a gene locus that appears to include 10 V genes, two D genes, two J genes, and one C gene. Mature γ/δ T cells seem to migrate primarily to mucosal and cutaneous tissues. The functions of γ/δ T cells are not yet understood. Moreover, the recognition of antigen by γ/δ T cells are not MHC-restricted.